David J. Schanzlin

Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study One Year After Surgery

The Prospective Evaluation of Radial Keratotomy (PERK) study is a nine-center, self-controlled clinical trial of a standardized technique of radial keratotomy in 435 patients who had physiologic myopia with a preoperative refraction between -2.00 and -8.00 diopters. The surgical technique consisted of eight incisions using a diamond micrometer knife with blade length determined by intraoperative ultrasonic pachymetry and the diameter of central clear zone determined by preoperative refraction. At one year after surgery, myopia was reduced in all eyes; 60% were within +/- 1.00 diopter of emmetropia; 30% were undercorrected and 10% were overcorrected by more than 1.00 diopter (range of refraction, -4.25 to +3.38 D). Uncorrected visual acuity was 20/40 or better in 78% of eyes. The operation was most effective in eyes with a refraction between -2.00 and -4.25 diopters. Thirteen percent of patients lost one or two Snellen lines of best corrected visual acuity. However, all but three eyes could be corrected to 20/20. Ten percent of patients increased astigmatism more than 1.00 diopter. Disabling glare was not detected with a clinical glare tester, but three patients reduced their driving at night because of glare. Between six months and one year, the refraction changed by greater than 0.50 diopters in 19% of eyes.

The Intrastromal Corneal Ring Segments: Phase II Results far the Correction of Myopia

OBJECTIVE The purpose of the study was to evaluate the safety and efficacy of the intrastromal corneal ring segments (ICRS) for the correction of myopia. DESIGN A 2-year phase II clinical trial of ICRS was initiated in May 1995. The investigational plan specifies that 150 patients with sighted eyes, requiring myopic corrections from -1.00 to -6.00 diopters (D), will each receive ICRS in 1 eye. The patient population will be divided into approximately five patients per ICRS thickness (0.25, 0.30, 0.35, 0.40, and 0.45 mm) per site. Six investigational sites are participating in the trial. PARTICIPANTS Fifty-nine men and 43 women requiring myopic corrections were enrolled at four U.S. investigational sites. These 102 patients each received the ICRS product in 1 eye. INTERVENTION Correction of myopia. MAIN OUTCOME MEASURES Efficacy of ICRS was assessed with respect to the trial endpoints of predictability of refractive effect, uncorrected visual acuity (UCVA), stability of UCVA, maintenance of best spectacle-corrected visual acuity and stability of refractive effect. RESULTS As shown by the available month-3 data (99 patients; all device thicknesses), 95 (96%) of 99 patients had a UCVA of 20/40 or better. Ninety-eight (99%) of 99 patients were within 2 lines of their preoperative best spectacle-corrected visual acuity. The average change (with standard error) in cycloplegic refraction (spherical equivalent) achieved by ICRS thickness was -1.27 +/- 0.09 D (0.25 mm), -2.13 +/- 0.16 D (0.30 mm), -2.56 +/- 0.15 D (0.35 mm), -3.77 +/- 0.37 D (0.40 mm) and -4.16 +/- 0.24 D (0.45 mm). Seventy-seven percent (76/99) of the patients were within +/-1.00 D of their intended correction. When the ICRS was removed in two cases, both patients returned to within 0.75 D of their preoperative manifest refraction. CONCLUSIONS The ICRS appears to be a viable and effective alternative for the treatment of myopia. Additionally, as indicated by the explant data, the ICRSs refractive effect may be reversible upon removal of the device.

Molteno Implant for Control of Glaucoma in Eyes after Penetrating Keratoplasty

Seventeen patients (17 eyes) underwent implantation of a single plate Molteno implant for medically uncontrollable intraocular pressures after penetrating keratoplasty. Most of the eyes had extensive peripheral anterior synechiae, and 16 of 17 (94%) were pseudophakic or aphakic following keratoplasty. Other glaucoma procedures had been performed previously on 13 eyes: argon laser trabeculoplasty (one eye), trabeculectomy (seven eyes), transpupillary argon laser cyclophotocoagulation (three eyes), and cyclocryotherapy (three eyes). Follow-up ranged from 5 to 28 months (mean, 13 months). Three eyes underwent repeat Molteno implantation when intraocular pressure (IOP) was not satisfactorily reduced after the first procedure. Considering one eye with chronic hypotony as a failure, 12 of 17 eyes (71%) had IOPs of less than 21 mmHg at the time of the three most recent postoperative examinations after a single Molteno implant. Repeat implants in three eyes increased the number of eyes with IOPs of less than 21 mmHg to 14 (82%). Corneal allograft rejection after Molteno implantation occurred in seven eyes; two of these were successfully reversed with corticosteroid therapy. Three of the five eyes with irreversible graft rejection were regrafted, and two of these grafts have remained clear. Including the regrafted eyes, 13 eyes had clear grafts and controlled IOPs at the most recent postoperative examination. The Molteno implant may prove useful in the management of medically uncontrollable glaucoma following penetrating keratoplasty; however, there appears to be a substantial risk of postoperative graft rejection.

Evaluation and comparison of sources of variability in the measurement of corneal thickness with ultrasonic and optical pachymeters

Two studies were carried out to determine and compare the effects of several sources of variation on the measurement of corneal thickness using the standard optical pachymeter and three ultrasonic pachymeters. Sources of variation included: intra- and inter-session variation, inter-observer variation, left/right eye variation, and variations due to alternate settings of ultrasonic sound frequencies. It was found that the optical pachymeter had a) two to three times as much intra-session variation as that of the ultrasound pachymeters, b) significant inter-observer variation (P = 0.015), and c) significant differences between left and right eye thickness determinations (P less than 0.005). On the other hand, ultrasonic pachymeters demonstrated a) high reproducibility, b) no inter-observer variation, and c) no left/right eye variation. These results have implications for the use of pachymetry in measuring corneal thickness for radial keratotomy and other refractive surgery.

Epidemiology of Microbial Keratitis in Southern California: A Multivariate Analysis

Two hundred twenty-seven cases of microbial keratitis reported in nonreferral county practice were studied. The staphylococci, Pseudomonas aeruginosa and Streptococcus pneumoniae, were the major isolates. A multivariate statistical model was developed to evaluate possible predisposing and outcome determinants. Several racial and age-related relationships were shown. The interaction of numerous local ocular and systemic factors played a fundamental role in causing disease. The authors found significant association between S. pneumoniae and topical steroid use, and direct and indirect linkage of S. aureus with diabetes and trauma, respectively. S. pneumoniae and Moraxella were risk factors for major complications (24% of cases); S. pneumoniae was related to enucleation and late perforation. Corneal exposure and prior topical steroids were associated with prolonged hospital stays. Hypopyon was associated with pneumococcal infection, 60 years of age or older, and trauma. The identification of groups at high-risk for microbial keratitis and problems of preventive management are discussed.

Pneumotonometry versus Goldmann tonometry after laser in situ keratomileusis for myopia

PURPOSE To assess the reliability of intraocular pressure (IOP) measurement by Goldmann applanation tonometry (GAT) versus pneumotonometry in patients after laser in situ keratomileusis (LASIK) for myopia. SETTING Shiley Eye Center, University of California San Diego, La Jolla, California, USA. METHODS In this prospective study, 31 eyes of 17 patients were evaluated before and 1 month after having LASIK for myopia. A masked observer measured preoperative and postoperative IOP by GAT centrally and by pneumotonometry at the center and the periphery of the cornea. Central corneal thickness and curvature were evaluated. RESULTS Preoperative IOP showed a good correlation between GAT and pneumotonometry values (r = 0.82). Mean postoperative IOP by GAT was lower by 3.8 mm Hg +/- 2.2 (SD) (26.3% +/- 15.2%) than by pneumotonometry: 2.3 +/- 2.8 mm Hg (15.4% +/- 10.7%) (P = .01). There were no statistically significant differences in central IOP versus peripheral IOP measured by pneumotonometry (P = .4). Regression analysis showed no statistically significant differences in IOP as a function of change in corneal thickness or change in corneal curvature with either device. CONCLUSION Postoperatively, there was a decrease in IOP measured by central GAT that was statstically significant. Differences in pneumotonometry were less substantial, with greater reliability of pneumotonometry than GAT after LASIK.

Ocular drug bioavailability from topically applied liposomes

During the past decade liposomes have been investigated extensively for their ability to improve drug utilization by the body, first in the area of chemotherapeutics and most recently in the area of ophthalmology. Liposomes are vesicle-like structures with a concentric series of alternating compartments of aqueous spaces and phospholipid bilayers. To date, liposomes have been found to both promote and reduce ocular drug absorption, indicating that a definite need exists for further studies to evaluate the interplay of drug, liposomes, and the corneal surface in determining the effectiveness of liposomes as vehicles for topically applied ophthalmic drugs. The purpose of this review is to place in perspective the role of liposomes in topical ocular drug delivery. As background material, the factors influencing ocular drug bioavailability and the features of liposomes pertinent to their effectiveness as drug carriers are reviewed.

Intrastromal corneal ring : 12-month sighted myopic eyes

BACKGROUND To evaluate the efficacy, predictability, and stability of the refractive effect produced by the Intrastromal Corneal Ring (ICR), the authors completed a 12-month study on 10 myopic eyes. METHODS Ten patients with preoperative refractive errors ranging from -2.63 diopters (D) to -4.25 D (mean, -3.30 D) participated in the study. The attempted correction was -2.50 D for a 7.0-mm diameter, 0.3-mm thick ICR. One eye of each patient received an ICR. RESULTS The average change in spherical equivalent at 12 months was -2.25 D (SD 0.54 D; range, -1.62 to -3.25 D). All patients maintained a spectacle-corrected visual acuity of 20/20 or better during the 12-month study period, with the exception of patient no. 6 who saw 20/30 at the 6-month examination. Her spectacle-corrected visual acuity returned to 20/20 a few days after the ICR was explanted and remained stable throughout the study. Uncorrected visual acuity had improved to 20/40 or better in all patients on postoperative day 1 and remained in this range for the 9 eyes (90%) during the 12 months of follow up. At postoperative month 12, 9 of 9 eyes (100%) had an uncorrected visual acuity of 20/40 or better with 3 of 9 eyes (33%) seeing 20/20 or better. The remaining patient, no. 6, experienced a tear in Descemets membrane during the procedure and required explantation of the ring after 6 months due to induced astigmatism and deterioration of uncorrected visual acuity. Two patients developed infiltrates that resolved with the use of antibiotics. The most common postoperative ocular findings were peripheral corneal haze in all eyes that diminished over time, minute lamellar channel deposits (7 of 10 eyes, 70%), deep stromal neovascularization (5 of 10 eyes, 50%), and pannus (5 of 10 eyes, 50%). CONCLUSION This preliminary study shows that implantation of an intrastromal corneal ring of this dimension (0.3-mm thick) can reduce approximately 1.50 to 3.00 D of myopia and maintain spectacle-corrected visual acuity.

Diurnal Change in Refraction, Corneal Curvature, Visual Acuity, and Intraocular Pressure After Radial Keratotomy in the PERK Study

Selected patients who complained of fluctuating visual acuity in the Prospective Evaluation of Radial Keratotomy (PERK) Study were examined before 8:00 a.m. and after 7:00 p.m. on the same day to determine diurnal change in uncorrected visual acuity, best corrected visual acuity, manifest refractive error, average central keratometric power, and intraocular pressure. Sixty-three operated eyes were examined at three months, while 46 operated and 40 unoperated contralateral eyes were examined at one year after radial keratotomy. One year after surgery, 42% of the operated eyes had an increase in minus power of the manifest refraction of 0.50 to 1.25 diopters, 26% of the eyes changed their uncorrected visual acuity by 2 to 4 Snellen lines, and 35% of the operated eyes showed central steepening of the cornea by 0.50 to 1.25 diopters. These changes in the operated eyes at one year were similar to the changes at three months. Minimal diurnal changes occurred in the unoperated eyes at one year. Only 11% of the unoperated eyes changed their manifest refraction by 0.50 to 1.00 diopters, none changed their uncorrected visual acuity by 2 to 4 Snellen lines, and only one of the unoperated eyes changed its central keratometric power by 0.50 diopters. This study documents that many patients who experience diurnal fluctuation of vision have steepening of the cornea and an increase in the minus power of their refraction during the day.

Results of Penetrating Keratoplasty For Aphakic And Pseudophakic Bullous Keratopathy

We retrospectively studied 61 consecutive cases of penetrating keratoplasty performed for aphakic bullous keratopathy or pseudophakic bullous keratopathy. After keratoplasty, the mean visual acuities of both groups of patients improved significantly from preoperative levels (P less than .0001). One year after keratoplasty, 18 eyes had visual acuities of 20/40 or better. Twelve of the 24 eyes followed up for at least two years after surgery had visual acuities of 20/40 or better. The mean visual acuities for the eyes with aphakic bullous keratopathy and the eyes with pseudophakic bullous keratopathy were not significantly different at either one or two years after keratoplasty. Cystoid macular edema (11 eyes) and glaucoma (12 eyes) were the most common causes of visual acuities worse than 20/40. There were no significant differences in the incidences of these complications in the group with aphakic bullous keratopathy and in the group with pseudophakic bullous keratopathy. Intraocular lens removal did not significantly affect either visual acuity or macular complications after keratoplasty.